Sink comment, NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219149 91177308-0d34-0410-b5e6-96231b3b80d8
LoopUnroll: Change code order of changes to new basic blocks

Add new basic blocks to `LoopInfo` earlier.  No functionality change
intended (simplifies upcoming bugfix patch).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219150 91177308-0d34-0410-b5e6-96231b3b80d8